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A New Unit of Measurement

A New Unit of Measurement. A Chemistry Exclusive!!. Dude!!!! Atoms are REALLY small!!!!!!. We can’t work with individual atoms or amu’s in the LAB Because we can’t see things that small.

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A New Unit of Measurement

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  1. A New Unit of Measurement A Chemistry Exclusive!!

  2. Dude!!!! Atoms are REALLY small!!!!!! We can’t work with individual atoms or amu’s in the LAB • Because we can’t see things that small.

  3. We work with samples large enough for us to SEE and WEIGH on a balance using units of grams.

  4. This creates a problem….. • A pile of atoms big enough for us to see contains billions of atoms. • Billions of atoms are hard to keep track of in calculations.

  5. So chemists made up new unit.. The MOLE

  6. What’s a MOLE? • It is a number of things • Just like a “dozen” • 1dozen eggs= 12 eggs • 1 mole eggs = 6.022 x 1023

  7. POP QUIZ • 1 dozen Mg atoms = 12 Mg atoms • 1 mole Mg atoms = 6.022 x 1023 atoms • 1 mole Mg(OH)2 = 6.022 x 1023 molecules • 1 mole O2 = 6.022 x 1023 molecules

  8. Everybody Dance Now!!! “Moleshake” My moleshake brings all the moles to the yard, And they’re like, “Man, Chemistry’s hard” Yeah right, yeah Chemistry’s hard, I can teach you, and I won’t even charge

  9. How Big is a Mole? • A mole of marbles would cover the entire Earth’s surface 50 MILES DEEP!!!

  10. How Big is a Mole? • If you spent a BILLION DOLLARS every second, you couldn’t spend a mole of dollar bills in your lifetime!!!

  11. Avogadro’s Number • 6.022 x 1023 is referred to as Avogadro’s Number - In honor of Amedeo Avogadro, Italian chemist (1776-1865) Ladies….. You know you want me.

  12. ….and if Avogadro rings, ask him to leave his number…”

  13. A “new” look at the periodic table… • We already know the periodic table tells us the mass (in a.m.u.’s) of a single atom • Ex. 1 Al atom has a mass of…. 26.9 grams Ex. 1 mole of Mg atoms has a mass of… 24.31 grams/mol

  14. So MASS on the periodic table has two meanings… • 1. When interpreted as grams/mole (g/mol) we call it “molar mass” • 2. When interpreted as amu’s (g) we call it “atomic mass” • The number doesn’t change, only the units.

  15. This also applies to molecules • The molecular mass of NH3 is… • The mass of 1 individual NH3 molecule 14.01 amu + 1.01 + 1.01 + 1.01 17.04 amu (g) of NH3 Or… 17.04 g/mol of NH3 if you are interpreting for molar mass.

  16. Practice Problems • 1. What is the atomic mass of Carbon? • 12.01 g or amu • 2. What is the molar mass of Carbon? • 12.01 g/mol • What is the molar mass of Mg3(PO4)2 ? • 262.87 g/mol • How many moles of Oxygen are in 1 mole of Mg3(PO4)2 ? • 8 moles of Oxygen

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